mobile: add README

mobile/README.md

@@ -0,0 +1,55 @@
+## Building mobile libraries
+
+### Prerequisites
+#### protoc
+Install the dependencies for genarating protobuf definitions as stated in [lnrpc docs](
+../lnrpc/README.md#generate-protobuf-definitions)
+
+#### gomobile
+Follow [gomobile](https://github.com/golang/go/wiki/Mobile) in order to intall `gomobile` and dependencies.
+
+Remember to run `gomobile init` (otherwise the `lnd` build might just hang).
+
+Note that `gomobile` only supports building projects from `GOPATH` at this point.
+
+#### falafel
+Install [`falafel`](https://github.com/halseth/falafel):
+```
+go get -u -v github.com/halseth/falafel
+```
+
+### Building `lnd` for iOS
+```
+make ios
+```
+
+### Building `lnd` for Android
+```
+make android
+```
+
+`make mobile` will build both iOS and Android libs.
+
+### Libraries
+After the build has succeeded, the libraries will be found in `mobile/build/ios/Lndmobile.framework` and `mobile/build/android/Lndmobile.aar`. Reference your platforms' SDK documentation for how to add the library to your project.
+
+#### Generating proto definitions for your language.
+In order to call the methods in the generated library, the serialized proto for the given RPC call must be provided. Similarly, the response will be a serialized proto.
+
+In order to generate protobuf definitions for your language of choice, add the proto plugin to the `protoc` invocations found in [`gen_protos.sh`](../lnrpc/gen_protos.sh). For instance to generate protos for Swift, add `--swift_out=.` and run `make rpc`.
+
+### Options
+Similar to lnd, subservers can be conditionally compiled with the build by setting the tags argument:
+
+```
+make ios tags="routerrpc"
+```
+
+To support subservers that have APIs with name conflicts, pass the "prefix" flag. This will add the subserver name as a prefix to each method name:
+
+```
+make ios tags="routerrpc" prefix=1
+```
+
+### API docs
+TODO(halseth)